The present invention is directed to an improved rotary shaft seal. In particular, the present invention is directed to a rotary shaft seal including a pair of seals used in a side-by-side arrangement wherein the seals have different coefficients of thermal expansion.
For certain applications Teflon(copyright) seals have been used as rotary shaft seals. Teflon(copyright) provides a seal which can be located within a shaft groove to provide a seal between the shaft and cylinder within which it is rotating. Such a seal reduces the coefficient of sliding friction and results in wear prevention between the shaft, inside surface of the cylinder and seal material. In applications where the seal retains hydraulic fluid pressure on one side thereof, the pressure forces the seal against the cylinder, and the groove within which the seal is located. This force is caused by the pressure drop across the seal. Due to fluid pressurization the seal will typically remain stationary relative to the cylinder and rotate relative to the seal groove in the shaft. The disadvantage of plastic or polymeric seals such as Teflon(copyright) seals is that they have thermal coefficients of expansion which are high relative to the metal shafts and cylinders with which they are typically associated. Accordingly, until a Teflon(copyright) seal is heated to a steady state operating temperature, the seal will provide a relatively poor seal against fluid flow. In other words, the gap created between the seal, cylinder and shaft in cold or transient temperatures will allow fluid to flow around the seal and create an undesirable pressure drop as a result thereof.
Rotary seals have also been fabricated from cast iron which has the advantage of having a thermal expansion substantially the same as steel shafts with which they are typically associated. When located within a groove in a rotary shaft, the seal normally will rotate with the shaft when pressure is created on one side of the seal because the coefficient of friction of cast iron relative to steel is much greater than that of Teflon(copyright) relative to steel. However, as a result of the higher coefficient of friction than Teflon(copyright), the cast iron seal will cause wear to the cylinder within which the shaft is rotating.
In view of the advantages and disadvantages of polymeric (e.g. Teflon(copyright)) and cast iron seals, it would be advantageous to selectively take advantage of the desirable performance characteristics of these seals to provide an improved rotary seal arrangement which is not subject to the undesirable performance characteristics of such seals.
One embodiment of the present invention provides a sealing arrangement for creating a seal between a first component such as a shaft having an exterior cylindrical surface and a second component such as a stationary hollow cylinder within which the shaft is located having an interior cylindrical surface. The arrangement includes a first circular seal fabricated from a first material having a coefficient of thermal expansion substantially greater than the first and second components, and a second circular seal fabricated from a second material having a coefficient of thermal expansion substantially the same as the first and second components. The first and second circular seals are positioned in a side-by-side relationship.
Another embodiment of the present invention provides a rotary seal arrangement. The arrangement includes a first component fabricated from metal and having an interior cylindrical surface, and a second component fabricated from metal and having an exterior cylindrical surface including a circumferential groove formed therein. A circular, polymeric seal is located within the groove, and a circular, metal seal is located adjacent to the polymeric seal within the groove. The second component is positioned relative to the first component such that the seals are adjacent to the interior cylindrical surface.
Another embodiment of the present invention provides a fluid porting arrangement for a transmission. The arrangement includes a stationary component fabricated from metal and having an interior cylindrical surface, a fluid port in the cylindrical surface and a fluid channel extending from an exterior surface of the stationary component to the fluid port. The arrangement also includes a rotary component rotatable within the stationary component, fabricated from metal. The rotary component has an exterior cylindrical surface including a circumferential porting groove aligned with the fluid port, a first circumferential groove formed on one side of the porting groove and a second circumferential groove formed on the opposite side of the porting groove. First and second circular, polymeric seals are located within the first and second circumferential grooves, respectively, and first and second circular, metal seals are located adjacent to the respective first and second circular polymeric seals in the respective first and second circumferential grooves.